1. Field
The present disclosure relates generally to a radio circuit used in wireless communication systems. More specifically, the present disclosure relates to a radio circuit with linearization-compensation capability.
2. Related Art
A recent decision of the Federal Communications Commission (FCC) has allowed unlicensed broadcasting devices access to “white spaces” in the television spectrum, prompting the development of the “WhiteFi” technology and white-spaces devices. Unlike traditional WiFi, which operates most commonly at 2.4 GHz and 5.0 GHz, white-spaces devices operate over 30 separate 6 MHz TV channels (freed after the conversion to digital TV) in the ultra-high frequency band (UHF). In order to protect licensed TV broadcasters from harmful interference, the FCC has required that the level of interference from adjacent channels needs to be less than −55 dBm. This requirement limits the amount of distortion or nonlinearity that can be tolerated by the power amplifier (PA), because an amplifier that compresses its input or has a nonlinear input/output relationship causes the output signal to splatter onto adjacent frequencies. In addition, to ensure good power efficiency of a device, it is important to maintain the linearity of the transmitter over a large dynamic range.
The linearity of a device can be improved by implementing a linearization algorithm based on a closed-loop system. Conventional technologies form a closed loop by building an off-chip feedback path, which is costly and impractical for compact mobile devices.